Article Information

• PDF (588 kb)

PubMed

• Articles by R.E. Godfrey

Related Articles

• Effects of Bleaching and Regeneration on the Purple Membrane...

  Effects of Bleaching and Regeneration on the Purple Membrane Structure of Halobacterium halobium Biophysical Journal, Volume 19, Issue 3, 1 September 1977, Pages 285-297 B. Becher and J.Y. Cassim Abstract Sequential bleaching in the presence of hydroxylamine and subsequent regeneration of the purple membrane of was studied by concomitant monitoring of its absorption and circular dichroic spectra in order to ascertain its effects on protein interaction(s) (which may result in possible excitonic interaction between the retinal chromophores), chromophore-apoprotein interaction(s), and protein conformational stability in the membrane. It was concluded that () although experimental results are consistent with an exciton mechanism for the interaction between retinal π - π* (NV) transition movements in the purple membrane, no evidence for such a mechanism for interaction between retinaloxime transition moments is apparent in the case of the bleached membrane; () the bacteriorhodopsin molecules organized in clusters of three in the membrane appear to bleach simultaneously; () the retinaloxime produced on bleaching the purple membrane in the presence of hydroxylamine is strongly optically active, because of dissymmetry-inducing and/or -selecting constraints on the chromophore by a component of the membrane (most likely the apoprotein), and when the membrane is regenerated by the addition of retinal, these constraints are lost; and () evidence from ultraviolet absorption and circular dichroic spectra suggests that the membrane apoprotein undergoes appreciable conformational changes involving tertiary structure on bleaching with no significant secondary structure involvement. These results are compared with recently reported results from this laboratory on the effects of bleaching on the bovine rod outer segment disk membrane structure. Abstract | PDF (771 kb)

• Unique biphasic band shape of the visible circular dichroism...

  Unique biphasic band shape of the visible circular dichroism of bacteriorhodopsin in purple membrane Biophysical Journal, Volume 63, Issue 5, 1 November 1992, Pages 1432-1442 Joseph Y. Cassim Abstract Over a decade and a half ago, when the first visible membrane suspension circular dichroic (CD) spectrum of the purple membrane (PM) was presented, two mechanisms were proposed to account for the observed biphasic shaped CD band: () excitonic interactions among the retinals of the sole protein bacteriorhodopsin (bR) in the crystalline structure of the PM, and () combination of CD bands with opposite rotational strengths due to a retinal-apoprotein heterogeneity of the bR molecules or due to two possible close-lying long-wavelength transitions of the retinal of the bR with opposite rotational strengths. Since that time, an impressive body of experimental and theoretical evidence has been accumulated, mostly consistent with an exciton model but many at serious odds with any heterogeneity or multiple transition model. Recently, a number of articles have appeared reporting analyses of new experimental observations which are proposed to cast serious doubts on the viability of the exciton model, and therefore, may revive the heterogeneity or multiple transition model as an explanation for the unique shape of the CD band of the PM. The intent of this article is to demonstrate that if all observations found in literature baring on this question are considered in toto and in a consistent manner, they can be interpreted without exception by excitons, and furthermore, that there is no plausible evidence available to warrant the revival of the heterogeneity or multiple transition model as an explanation for the unique shape of the biphasic CD band of the PM. Abstract | PDF (1340 kb)

• Circular Dichroic Spectrum of the L Form and the Blue Light ...

  Circular Dichroic Spectrum of the L Form and the Blue Light Product of the M Form of Purple Membrane Biophysical Journal, Volume 51, Issue 1, 1 January 1987, Pages 145-148 László Zimányi, Zsolt Tokaji and Gavin Dollinger Abstract Simultaneously measured low temperature absorption and circular dichroic spectra are presented for different intermediates of the bacteriorhodopsin photocycle in suspension and hydrated film of purple membranes. The data for the L intermediate are in accord with excitonic interpretation of the visible part of the circular dichroic spectrum, suggesting that no large scale structural change of the purple membrane affecting its crystalline structure happens during the L formation. The structure of the membrane, which is disrupted in the M state, is recovered when M is illuminated with blue light at low temperature. Abstract | PDF (366 kb)

• …more

Abstract

The transient dichroic ratio D = delta A parallel/delta A perpendicular has been measured in the visible absorption region of bacteriorhodopsin in purple membrane by a flash photolysis method. D is found to be wavelength independent throughout the visible absorption band, and reaches a maximum value of 2.75 +/- 0.15 on reduction of the excitation intensity. This value is close to that expected for a single nondegenerate transition dipole moment and is incompatible with the strong exciton coupling model used to explain circular dichroism (CD) spectrum of purple membrane. A time-dependent analysis of the exciton interaction and consideration of the coupling strength suggests an explanation of these observations. It is concluded that excitation interaction between retinals in purple membrane is of the weak or very weak type defined by Förster.